Ink jet inks many times provide marginal print quality. This is so, because water-based ink jet inks generally have poor penetration and drying characteristics with respect to the paper.
On the other hand, oil-based inks have low surface tension and usually provide ink dots which are too large to give good print quality.
The present invention seeks to formulate ink jet inks which can provide small, circular dots on many paper media. These small circular dots will produce characters having good edge definition, and contrast, and hence, characters of good print quality.
The present invention proposes to use stearic acid as a major base component of ink jet inks. The stearic acid of this invention may be considered a synthetic wax or a natural wax.
Commercial stearic acid is not a chemically pure compound, but a mixture of fatty acids in which stearic acid predominates.
Stearic acids are chiefly produced from saponified and distilled animal fatty acids. These fatty acids are usually composed of approximately 60% liquid and 40% solid acid. The bulk of the liquid acids is separated from the solid acids by hydraulic pressing. From the first pressing single-pressed stearic acid is obtained, from the second pressing, double-pressed stearic acids, and from the third pressing, triple pressed stearic acids. Each successive pressing removes additional liquid fatty acids, thus increasing the purity and quality of the resulting solid stearic acid. The liquid acids present are unsaturated and the solid acids, saturated.
Wax-containing ink jet inks are usually solids or semi-solids at ambient temperature, and therefore, require to be discharged from an ink jet apparatus at elevated temperatures. The heated ink fluid will solidify when it comes in contact with its paper target. The rate of solidification of the wax-containing ink will control the degree of penetration into the paper, usually a small circular dot will result. As a general rule, inks containing wax as a major component thereof, will have less penetration into the paper than inks containing additive amounts of wax.
A definition of "waxes" can be found in Industrial Waxes by H. Bennett; Volumes 1 and 2; Chemical Publishing Company, Inc., New York, NY (1975). Bennett defines a wax as "an unctuous solid with varying degrees of gloss, slipperiness and plasticity, which melts readily".
Natural waxes may be of vegetable, animal, or mineral origin. Modified waxes are natural waxes that have been treated chemically to change their nature and properties. Synthetic waxes are made by the reaction or polymerization of chemicals. Compounded waxes are mixtures of various waxes or of waxes with resins or other compounds added thereto.
There is considerable misunderstanding as to the nature and classification of fats, waxes, gums, and resins. For example cocoa butter, although it is actually a fat, is commonly considered as a wax because of certain characteristic properties. On the other hand, wool wax, derived from lanolin, is technically a wax but, because of its properties, it is usually considered as a fat. Kauri gum is commonly called a wax; and so on.